The invention relates to a feed dog drive having an adjustable feed direction for a sewing machine.
A feed dog drive having an adjustable feed direction is described, for example, in Italian Patent Specification No. 63 01 70. Although this feed dog drive allows the workpiece to be fed in a straight line between two needle holes in any direction and in continuous sequence, it is not suitable for exerting a rotary motion on the workpiece. Such a rotary motion is, however, necessary in order to execute, for example, a so-called safety seam, which is made by two adjacently disposed needles, along a curved edge of a workpiece. In Italian Patent Specification No. 63 01 70, two motions, which are at right angles to one another and whose magnitude and direction can be regulated, are superimposed on the feed dog carrier, so that the resultant motion can be attained in any direction required. If feed adjustment is constant, the resultant feed motion is in a straight line. Even if the feed direction of the feed dogs is constantly being changed, no rotary motion is exerted on the workpiece, but rather stepwise linear feeding takes place in different directions.
A further direction-controlled feed dog drive is described in German Auslegeschrift No. 1 485 403 corresponding to U.S. Pat. No. 3,116,705. In this feed dog drive, two feed dog elements, whose feed magnitudes are adjustable independently of one another, are disposed adjacent to one another. The feed dog element adjacent to an edge guide carries out a larger feed motion than the other feed dog element, and presses the workpiece against the edge guide. The varying feed motion of the feed dog elements causes the workpiece to pucker. The surface of delicate workpieces is damaged, as the feed dog element carrying out the larger feed motion compared with the other rubs against the workpiece.